Introduction to Structured Light

Good afternoon everyone,

I'm going to try to blog at least one a week about useful projects and things that I've been working on.  Today I'm going to do a high level discussion about how structured light works and how to make your own profilometer.

A profilometer is a device that uses a beam of light and a camera to measure depth.  They can be tuned to work with many different working ranges and resolutions.  Some can measure surfaces to within 0.01mm accuracy.

The range calculation for a profilometer comes from something called triangulation.  Triangulation is the calculation of the parameters of a triangle created between the camera and the laser beam.

A great resource on this topic is the Build Your Own 3D scanner course from Brown University. They have a set of course notes that's nearly a book where I learned quite a bit.

In summary, to create your own profilometer you'll need the following hardware:

1) Camera (I used a Logitech C920)
2) Laser source 
3) Digital servo motor (Can be had for as low as $10 from sparkfun.com)
4) Mounting hardware and a way to control the motor
My setup looks like this:

The kinect is for other uses.

I'm going to assume you can figure out how to mount everything and how to control a digital servo, so on to the fun.
What you'll need to do to make an accurate scanner is the following:
1) Calibrate the camera
2) Calibrate the laser to the camera
3) Calibrate the motion of the camera due to the servo

Intro

My name is Daniel Moodie and I'm a computer vision programmer for the Mechatronics Lab of Virginia Tech.  I work on developing various computer vision algorithms for Autonomous and tele-operated robots. I am particularly interested in perception and 3D scene reconstruction.  My thesis pertains to 3D scene reconstruction for inspection purposes.